1. Field of the Invention
The present invention relates to a ferrite magnet device, a nonreciprocal circuit device including the ferrite magnet device, and a composite electronic component including the nonreciprocal circuit device. The nonreciprocal circuit device may be an isolator or a circulator, for example, used in a microwave band.
2. Description of the Related Art
Typical nonreciprocal circuit devices, such as isolators or circulators, have a characteristic in which a signal is transmitted in a predetermined specific direction and not transmitted in the reverse direction. To utilize this characteristic, an isolator, for example, is used in the transmitter circuit unit of a mobile communication apparatus such as a vehicle telephone or a cellular phone.
Usually, such a nonreciprocal circuit device includes a ferrite magnet device including a ferrite element having central electrodes provided thereon and a permanent magnet arranged to apply a direct current (DC) magnetic field to the ferrite element, and a predetermined matching circuit device including a resistor and a capacitor. A module, such as a composite electronic component having a plurality of nonreciprocal circuit devices or a composite electronic component including a nonreciprocal circuit device and a power amplifier device, is also currently available.
Various nonreciprocal circuit devices have been proposed in Japanese Unexamined Patent Application Publication No. 2002-299912, Japanese Patent No. 3649162, Japanese Unexamined Patent Application Publication No. 2007-208943, for example. The nonreciprocal circuit devices described in Japanese Unexamined Patent Application Publication No. 2002-299912 and Japanese Patent No. 3649162 require complex assemblies, which cause variations in characteristics due to deviations in the assembly, since the permanent magnet and ferrite element having central electrodes are not combined. The nonreciprocal circuit device described in Japanese Patent No. 3649162, in particular, has a problem in which the central electrodes that are made of a photosensitive conductor paste undergo shrinkage after sintering, and thus, the precision is limited due to variation in the degree of shrinkage.
In the nonreciprocal circuit device described in Japanese Unexamined Patent Application Publication No. 2007-208943, the ferrite element including central electrodes is supported by a pair of permanent magnets so as to be combined with the permanent magnets. Thus, the problem of assembly deviations is solved due to this simple configuration. However, the problem of variation in the degree of shrinkage has not been solved since the central electrodes require sintering.